Studies this year have centered about how the ovary and the hypothalamic-pituitary unit interact in women. We have shown that the hypothalamic release of GNRH is modulated by both estrogens and progestins of ovarian origin. The mechanism of modulation has been clarified. It has been shown that the ovary signals the hypothalamic-pituitary unit when it has a dominant follicle ready for ovulation, and that the signal is progesterone from the dominant follicle. The mechanism of the preovulatory progesterone surge has been clarified.